I. Field of the Invention:
The present invention relates generally to a bypass and unloader valve for use in fluid handling systems, and more specifically to an improved design of such a valve which permits its use over prolonged periods of time in systems involving relatively high fluid pressures.
II. Discussion of the Prior Art:
In my earlier U.S. Pat. No. 4,171,708 there is described a bypass and unloader valve which is designed for use in fluid handling systems in which the discharge of a fluid may be intermittently shut off. In such systems, a pump may be used to deliver liquids at high pressure to one or more outlet nozzles for providing a high pressure spray at a plurality of sites. For example, in a coin operated car wash application, a common pump may be used to deliver water or other chemicals to spray guns located in separate stalls. At any given time, all, less than all or none of the spray guns may be operating and, as such, means must be provided for unloading the liquid to a bypass so that the pump is not subjected to undue back pressure. While the unloader valve of my aforereferenced patent is entirely suitable for fluid handling systems wherein the pressures encountered are relatively low or intermediate, that design is not altogether suitable in systems involving relatively high pressures. For example, it will be noted from my earlier patent that the valve stem or plunger is maintained in tension by a heavy spring element and for the bypass valve to operate, the plunger must be made to move against the force of this spring as the outlet pressure increases. Where high fluid pressures are involved, the force becomes so significant that the plunger member may fail in tension. While this can be avoided by designing a plunger of a large diameter, this necessarily increases the size, weight and cost of the unloader valve. Then too, the cup seal on the piston element secured to the plunger will be extruded between the mating surfaces of the piston and cylinder side walls causing leakage and deteriorated performance which may require frequent repair, depending upon the pressures encountered.